There are some known safety devices for protecting occupants in a vehicle from an impact of a collision, having a squib which is actuated by a electric current flowing through it. One of them is the safety device which uses an airbag which is inflated during a collision, and another of them is the safety device which uses a pretensioner of a seat belt which winds the seat belt at a collision so as to draw the occupants up to the back of the seat. A driver's seat is provided with the above airbag and the above pretensioner of the seat belt. And a passengers' seats is also provided with the airbag and the pretensioner of the seat belt.
In recent years, great importance is attached to the safety of occupants in a vehicle. Consequently, there is a growing tendency toward providing a vehicle with a plurality of safety devices for protecting the occupants. There is one idea that one actuater is provided to each of a plurality of squibs in a plurality of safety devices respectively. However, it is generally thought that all the squibs are actuated by a common actuater in order to reduce the number of parts and thereby make the cost concerning the safety devices inexpensive.
In case that a plurality of squibs are actuated by a common actuater, it is necessary to energize all of the squibs with certainty in a shortest time. Therefore, all of the squibs are connected in parallel with each other, and a parallel circuit resulting therefrom is connected to a power source such as a capacitor charged by a battery. In case of the parallel circuit, if one of these squibs is short-circuited, it will result in no current flowing through the remaining squibs. This problem is overcome by providing each squib with current limiter means such as a resistor. Consequently, an amount of a required current at the power source becomes large by reason that the total amount of a current from a power source into all squibs is equal to the sum of the currents of each squib with a resistor. As a result, the power source increases in volume and weight. This is one of factors that prevents the actuater from decreasing in size and weight.
In a further previously proposed arrangement, as described in the Japanese Laid Open Patent Application No. 4-147846, there is an apparatus for actuating the safety devices comprising a plurality of squibs connected in series with each other so as to form a series circuit which are connected to a power source, and a plurality of bypass means connected respectively to the plurality of squibs in parallel, where a current flows through the bypass means when the series circuit opens electrically at one squib. The bypass means are required by reason that the current will not flow through the remaining squibs if the series circuit opens electrically at one squib without bypass means. The bypass means may consist of a voltage regulation diode or a transistor circuit. This prior apparatus has a effect that an amount of required current for a plurality of squibs connected in series with each other is less than that for squibs connected in parallel with each other.
However, This prior apparatus has a problem that the number of parts increases because each squib is provided with the provision of bypass means such as a voltage regulation diode or a transistor circuit. This is one of factors that prevents the apparatus for actuating the safety devices from decreasing in size and weight.
In view of the above-described problems, it is an object of the invention to provide an apparatus for actuating the safety devices for vehicle occupants, comprising a plurality of squibs included in a plurality of safety devices for vehicle occupants respectively, which are connected in series with each other so as to form a series circuit, and a power source connected to the series circuit, wherein all squibs are ignited with certainty even if the series circuit is broken at one squib without bypass means connected in parallel with the squib.